Internal Metadata Backups
DEVONthink does not have a system for automatically backing up everything. DEVONthink has a setting in its Preferences > Backup that controls how many internal metadata backups are done. These backups can be used in a troubleshooting situation by selecting Tools > Restore Backup.
While it may seem like a good idea to set this to something like seven copies daily, the metadata of a database can be considerable, so you should be cautious in how you set this. It's not a performance issue, but you will be increasing the size of the database packages with a higher number of backups.
To backup everything including the data files we strongly advocate using Time Machine and local external drives or Arq for online archiving. — And as a persistent reminder, do not put your databases in any cloud-synced folder!